feat(tholos-v2): add set_admin rotation path and AdminUpdated event (#129)

[s6pa1rta3n-lab]

Closes #129

Summary

• Implemented set_admin(env: Env, new_admin: Address) -> Result<(), Error> on TholosV2.
• Enforces current admin authorization via admin.require_auth().
• Verifies contract is initialized, returning Error::NotInitialized if uninitialized.
• Updates DataKey::Admin in instance storage.
• Extends instance TTL with INSTANCE_LIFETIME_THRESHOLD and INSTANCE_BUMP_AMOUNT upon every successful rotation.
• Emits AdminUpdated { old_admin, new_admin } event upon rotation.
• Pause-exempt by design: admin key rotation is callable while paused to support key recovery and migration during emergency freezes.
• Added comprehensive unit tests in contracts/tholos-v2/src/test.rs:
  • test_admin_can_rotate_admin
  • test_old_admin_loses_authority_after_rotation
  • test_set_admin_emits_event
  • test_set_admin_is_pause_exempt
  • test_cannot_set_admin_before_initialization
  • test_set_admin_extends_instance_ttl
• Updated documentation in docs/src/CONTRACT_V2.md, docs/src/INTEGRATION.md, and added an admin key rotation runbook in docs/src/DEPLOYMENT_V2.md.

Payout Routing

• EVM (Base/Arbitrum/Polygon/ETH): 0xF46C9F6d70C50BF81ef3588AB523a90a594a2F89
• Stellar: GCL6OXAMLD75BMTINA6EMRUDWK5THQUSHMYNLSNBCJAPZJHNYJTUNIBC

[collinsezedike]

@s6pa1rta3n-lab Closing — #129 is assigned to dimin4241-svg, not you.